Plastic modal approximations in analyzing beam-on-beam collisions

Dynamic behavior of a moving free-free beam striking the tip of a cantilever beam, as a typical example of collision between two deformable structures, is analysed by employing modal approximation techniques. The applicability of both rigid-plastic and elastic-plastic mode approximations is examined in predicting the energy partitioning between the two colliding beams. Three rigid-plastic modes (RP-Modes) are considered and the Lee's functional is applied to select the appropriate mode. It is found that one of the beams would absorb all the initial kinetic energy, unless a higher-order RP-mode is adopted. To incorporate the effect of elastic deformation into the modal solution, an elastic, perfectly plastic mode (EP-Mode) approximation for the same problem is proposed. By replacing each of the plastic hinges in the RP-Mode with a nature hinge and an elastic-plastic rotational spring, the fundamental features of the dynamic elastic-plastic behavior of the two colliding beams are revealed. Both beams participate in energy dissipation, while the structural and geometrical parameters greatly influence the energy partitioning. It is shown from numerical examples that the EP-Mode solution provides a fairly good approximation compared with the RP complete solution and finite element simulation.